In the homopolymerization of 1,3-dienes, as well as in their copolymerization with one another or with other monomers, e.g., vinyl-substituted aromatics, polymers are obtained having isolated double bonds in the primary chain.
However, it is known that low and high molecular weight compounds with conjugated double bonds are superior with respect to reactivity, and thus also attractiveness, to the corresponding compounds having isolated double bonds. For this reason, processes have been developed for the production of compounds with conjugated double bonds. Suitable procedures, in this connection, include, for example, copolymerization of 1,3-dienes with acetylene [J. Furukawa et al., Journ. Polym. Sci., Polym. Chem. Ed. 14: 1213-19 (1976)]. Another, and more economical, possibility is the isomerization of isolated double bonds to conjugated double bonds. To conduct this isomerization, a great variety of different catalyst systems has been utilized.
Thus, DAS No. 1,174,071 discloses a process for the isomerization of butadiene polymers wherein the butadiene polymers are heated to temperatures of between 100.degree. and 300.degree. C. in the presence of small amounts of transition metals of Groups VI through VIII of the Periodic Table of the Elements and/or of compounds wherein these metals are present in the zero valence state. The disadvantages of this process reside in the relatively high cost of the isomerization catalysts and their lack of handling ease. Moreover, they effect cis-trans isomerization which leads to the loss of reactive cis-1,4-structures.
Furthermore, according to the process described in DOS No. 2,342,885, the combination of an organic alkali metal compound and a specific diamine is usuable as the isomerization catalyst for low-molecular weight homo- and copolymers of butadiene. The chelating effect of the diamines employed results, however, in a relatively high content of alkali metal ions in the polymer. This has an adverse influence, for example, when this polymer is used in the varnish (paint) sector. Furthermore, the combination of polymerization and isomerization, described as preferred, does not yield the high content of cis-1,4-structures advantageous for the drying properties of low-molecular weight polybutadienes.
Also, German Pat. No. 1,156,788 and DAS No. 1,156,789 disclose processes for converting fatty acid esters of monohydric alcohols with isolated double bonds into fatty acid esters having conjugated double bonds wherein alkali metal alcoholates are utilized as the isomerization catalysts.
The application of these processes to other classes of compounds could not be expected, at least for the reason that the isomerization activity recedes markedly even if merely transferred to esters of polyhydric alcohols, such as, for example, naturally occurring oils.
In this respect, it was surprising to find it possible to convert isolated double bonds into conjugated double bonds in homo- and/or copolymers of 1,3-dienes, using sodium and potassium alcoholates. See DOS's Nos. 2,924,548.5, 2,924,598.5, 2,924,577.0 and 3,003,894.9 and its U.S. equivalent Ser. No. 160,807 of June 19, 1980, now abandoned, and DOS No. 3,003,872.3 and its U.S. equivalent Ser. No. 230,826 of Feb. 2, 1981, now abandoned, all of whose disclosures are incorporated by reference herein. Such unsaturated polymers are substantially different from the fatty acid esters (1,4-diene structures) with regard to the position of the double bonds (1,5-diene structures).